Limiting electric strength of vacuum electrode systems including combined breakdown

There exists three types of emission sites, eventually being a place of initiation of electric breakdown in vacuum switching devices with a screened insulator. Using electrostatic field calculations, potential breakdown paths, which start at the emission site in a vacuum interrupter, have been analyzed. Combined breakdown includes a breakdown path across two vacuum gaps and formation of flashover along an insulator. The paper discusses physical models of electron current multiplication at the insulator surface leading to the breakdown initiation.